Heat-sensitive recording materials using a color reaction between a leuco dye and a developer are well known. The heat-sensitive recording materials are relatively inexpensive, and the recording apparatuses are compact and easily maintained. Therefore, heat-sensitive recording materials are used not only as recording media for facsimiles, a variety of calculator, and the like, but also as recording media for the printers of medical image diagnosis apparatuses, recording media for CAD plotters, and the like.
Among the various heat-sensitive recording materials, those used as medical apparatus recording media used with schaukastens require high transparency and recording density. Therefore, in these heat-sensitive recording materials used as recording media of medical apparatus, the thermal energy of the thermal head increases, thereby more easily causing sticking or noise during the recording. To solve this problem, a general heat-sensitive recording layer has a protective layer thereon.
As one general technique for improving the water resistance of the protective layer, Patent Literature 1 discloses a heat-sensitive recording material that uses acetoacetyl-modified polyvinyl alcohol as the adhesive of the protective layer, and contains a hydrazine-based compound as a water-resistant agent in the heat-sensitive recording layer. Further, Patent Literature 2 suggests providing an intermediate layer containing a water-soluble resin as the main component on the heat-sensitive recording layer in order to prevent the heat-sensitive recording layer from mixing with the protective layer, thereby preventing a decrease in transparency. However, these prior arts could not guarantee satisfactory effects, particularly in terms of the desired transparency, water resistance and heat resistance required for image-recording media of medical image diagnosis apparatuses.